nickserv: grouped nicks (GROUP/GLIST/UNGROUP) and GHOST

A nick can be grouped to an account and then identifies to it; the store
resolves an alias to its account everywhere it authenticates. GHOST (and
RECOVER) rename off a session using a nick you own. Grouped nicks
federate and are dropped with their account.

modules/nickserv/glist.rs

@@ -0,0 +1,17 @@
+use crate::engine::db::Db;
+use crate::engine::service::{Sender, ServiceCtx};
+
+// GLIST: list the nicks grouped to your account.
+pub fn handle(me: &str, from: &Sender, ctx: &mut ServiceCtx, db: &Db) {
+    let Some(account) = from.account else {
+        ctx.notice(me, from.uid, "You need to be logged in. Identify to NickServ first.");
+        return;
+    };
+    let mut nicks = db.grouped_nicks(account);
+    nicks.sort();
+    ctx.notice(me, from.uid, format!("Nicks grouped to \x02{account}\x02:"));
+    ctx.notice(me, from.uid, format!("  \x02{account}\x02 (main)"));
+    for n in nicks {
+        ctx.notice(me, from.uid, format!("  \x02{n}\x02"));
+    }
+}